The invention relates to an apparatus for obtaining information on the motion of a moving element, preferably for determining the speed and position of a rotating element. Various kinds of apparatus for obtaining speed information are known. In a conventional arrangement for measuring revolutions per minute (rpm) of a rotating gear, a sensor near the teeth of the gear detects magnetic irregularities and transmits these irregularities as electrical signals to an evaluation circuit that determines the rpm of the gear from the electrical signals. However, such kinds of apparatus are affected by external electrical signals or noise which is picked up during the transmission of electrical signals from the sensor to the evaluation circuit. But such apparatus may transmit speed information with light signals in lieu of electrical signals from the sensor to the evaluation circuit to reduce electromagnetic interference. The apparatus may even have a self-powered sensor which detects the magnetic irregularities and transmits signals via light signals. The disadvantages of this apparatus is that the light signal generation and information conveyance capacity are notably inefficient.